a. Field of Invention
The invention relates generally to fatigue testing, and more particularly to a method and apparatus for fatigue testing springs and other such devices.
b. Description of Related Art
Single story coil fatigue test systems are generally used in the art to fatigue test coil springs and other such devices. As disclosed in JP 410260122A, and further in U.S. Pat. No. 2,350,722, the disclosure of which is incorporated herein by reference, conventional spring fatigue test systems generally include a fatigue testing machine similar to the one disclosed in FIG. 1 herein. Referring to FIG. 1, conventional fatigue testing machines generally include a mechanism 10 driven into one or more mounted coil springs 12 repeatedly using hydraulic, electrical or pneumatic power until the spring fatigues, or a cycle criteria has been achieved. The force of driving mechanism 10 in such a conventional system must however be constant in order to compress spring 12 from highest (i.e. rebound) to lowest (i.e. jounce) height positions. Accordingly, the number of springs which may be tested in a conventional fatigue test system at any given time is limited primarily by the driving capacity of the system.
The prior art also includes spring fatigue testing machines for testing multiple springs in a given testing cycle. For example, as disclosed in U.S. Pat. No. 2,381,241, the disclosure of which is incorporated herein by reference, there is disclosed in FIG. 1 a circular spring testing machine for testing springs A disposed on rods 30 and compressible by rotary ring 46. While the mechanism disclosed in the '241 patent enables testing of multiple springs, it is nevertheless limited to compression as opposed to compression/tension testing of multiple springs. Moreover, due to the requirement for adjustment of numerous levers and guides, in operation, the mechanism disclosed in the '241 patent is completely impractical for high speed and repeatable spring testing, as is required in today's automotive and other mass manufacturing environments.
In an improvement to the mechanism of the '241 patent, SAE Tech Paper No. 900663 (hereinafter “SAE '663”), titled “A New High Speed Suspension Spring Test Mechanism,” discloses an additional circular fatigue testing machine for testing multiple springs. For the mechanism disclosed in SAE '663, coil springs are each setup individually around a rotating cam, which compared to the mechanism of the '241 patent, pushes and pulls the various rods to compress the springs. As discussed above for the mechanism of the '241 patent, although the device of SAE '663 can test multiple springs at once, the SAE '663 mechanism also includes several drawbacks and limitations. For example, since each spring for the SAE '663 mechanism must be mounted individually, setup time for testing becomes a significant factor when testing multiple springs. Furthermore, the load savings relationship between each spring and its adjacent counterpart is hindered due to the multiple forces being applied by the other springs mounted at different angles.
Yet further, as disclosed in U.S. Pat. No. 2,222,892, the disclosure of which is incorporated herein by reference, there is disclosed in FIGS. 2 and 3 a multiple spring testing mechanism including springs 19 mounted on fixed plates 11, 21, and further mounted on oscillating beam 14. In operation, as beam 14 is oscillated by means of crank mechanism 15, 16, as discussed in Col. 2:35-38, due to the uneven oscillation in the left-most versus the right-most springs, the right-most springs tend to break faster than the left-most springs. It therefore becomes readily apparent that the fatigue testing results generated by the mechanism of the '892 patent are extremely difficult to comprehend, in that the location of the springs on the mechanism, as well as the degree of crank of mechanism 15, 16, which is adjustable at slide block 17, must be taken into account for determining the life cycle of a left-most spring, as opposed to a central or a right-most spring.
It would therefore be of benefit to provide a fatigue test system with increased capacity of testing the compression and tension cycles of springs and other such devices, without increasing the force needed to drive the springs. It would also be of benefit to provide a fatigue test system which can reduce the overall driving force needed per test cycle, which can favorably eliminate any resistance to the driving mechanism that may be produced by the springs during neutral conditions, and for which the testing technique and results are repeatable and simple to interpret. There thus remains a need for a fatigue test system, which is robust in design, efficient to operate, simple to assemble and disassemble, and which is economically feasible to manufacture and utilize.